With the recent trend toward a decrease in the fuel consumption of automobiles for the purpose of saving of resources, energy conservation, and a decrease in emission of carbon dioxide, there has particularly been a demand for a decrease in the weight of automobile parts.
Conventionally, in order to decrease the weight of various materials formed of metal, the metal has been replaced by resin materials having a lower specific gravity than the metal, in particular, polyamide-based materials. However, polyamide-based materials have lower heat resistance, compared with metal materials. For this reason, polyamide-based materials are limited for their usage. Thus, there has been a demand for a resin material having higher heat resistance.
In particular, regarding automobile parts that are ducts within engine rooms, conventional aluminum materials have been replaced by blow-molded hollow articles formed of resin materials. Currently, polyamide-based materials are mainly used. However, since the members are mainly exposed to exhaust gas, polyamide-based materials are insufficient in terms of heat resistance. For this reason, there has been a demand for a blow hollow molding material that has high heat resistance and also has chemical resistance and impact resistance.
Thus, use of an engineering plastic excellent in terms of heat resistance, chemical resistance, flame resistance, electrical characteristics, and the like, a polyarylene sulfide resin (hereafter, sometimes abbreviated as a PAS resin), has been studied not only for automobile parts but also for various applications including electrical or electronic components and precision machinery components. However, molded articles formed of the polyarylene sulfide resin are known to be brittle. Although such molded articles are provided so as to have impact resistance by addition of various fillers, they are still insufficient as replacements for metal materials.
In particular, various attempts have been made for a long time for use of blow hollow molding materials using a polyarylene sulfide resin. However, when molding a polyarylene sulfide resin, it has extremely high melt fluidity, and thus in normal extrusion blow molding, that is, in a method of extruding and blow-molding a parison, there is a problem in that draw-down of the parison extremely increases, and it is very difficult to mold the parison into a container having small thickness unevenness. Accordingly, the use of the polyarylene sulfide resin is mostly limited to an injection molding method, and most of the molded articles of the polyarylene sulfide resin have small sizes. The application of the polyarylene sulfide resin to large-sized components such as bottles and tanks provided by blow molding or the like has been rarely performed.
As an example of the application of the polyarylene sulfide resin to blow molding, there is a known resin composition obtained by melting and kneading a polyarylene sulfide resin and an epoxy group-containing olefin-based copolymer (PTL 1). However, although the polyarylene sulfide resin has a high melt viscosity, it has a high proportion of terminal carboxy groups, and contains a large amount of low-molecular-weight components. For this reason, there is room to improve moldability of the composition in terms of draw-down resistance and thickness unevenness in performing the blow hollow molding. In addition, there is also room to improve the mechanical strengths, particularly, thermal shock resistance particularly because of a high proportion of the reaction products between the low-molecular-weight components of the polyarylene sulfide resin and the epoxy group-containing olefin-based copolymer. Thus, the composition has not yet been used under more harsh environments such as in regions including automobile engines.
There is a known blow-molded hollow article excellent in moldability and mechanical strengths such as thermal shock resistance, which is provided by the combination of a high-molecular-weight linear polyarylene sulfide resin having a specified concentration of terminal carboxy groups and an olefin-based polymer (PTL 2). However, while use of the olefin-based polymer can impart mechanical strengths such as impact resistance to blow-molded hollow articles containing the polyarylene sulfide resin, it also causes degradation of the heat resistance. For this reason, there has been a demand for a blow-molded hollow article that is excellent in mechanical strengths such as impact resistance while maintaining excellent heat resistance of a polyarylene sulfide resin.